1. Field of the Invention
This invention is directed to fertilizers and methods for treating biosolids such as organic-containing sludges and alkaline materials thereby converting them into useful inorganic-organic nutrient fertilizers. The invention is also directed to treatment of sludges or biosolids to reduce noxious odorants prior to drying steps in manufacture of organic containing fertilizers.
2. Description of the Background
There are a number of methods currently available for converting organic materials into fertilizers. Examples of such organic materials include, animal residuals and manures, sewage sludge, lagoon sludges, pharmaceutical fermentation sludges, food fermentation sludges and other microbial digested organic materials such as blood meal, fish by-products and meal, food wastes, food processing wastes and animal remains such as slaughterhouse wastes (all hereinafter referred to as “biosolids”).
When these organic-containing materials are manufactured into fertilizers, very often they contain low levels of the important plant nutrients, nitrogen, phosphorus and potassium. This limits their usefulness and marketability in commercial agriculture which applies value to a fertilizer based upon its nutrient content, especially the nitrogen and phosphorus concentrations in dry weight. This is especially true of products manufactured from municipal biosolids as the nitrogen level in biosolids on a dry weight basis is usually 3 to 5 percent. The implications of a low fertilizer nutrient level are low market value with concomitant limitations on the distance these materials can be transported from their manufacturing site. In contrast, high nitrogen fertilizers (products containing over 8 percent nitrogen by dry weight and especially products over 12 percent nitrogen by dry weight) can be transported thousands of miles to wholesale and retail markets.
A few organic products can be purchased “fortified” for a higher nutrient analysis. The ingredients used to fortify organic fertilizers are generally inorganic fertilizer components which because these already are fertilizers are expense, for example, ammonium nitrate, ammonium sulfate, ammonium phosphate or urea and various sources of potash (potassium) such as potassium oxides and greensand.
Organic fertilizers depend on soil organisms to break them down to release nutrients; therefore, most are effective only when soil is moist and warm enough for the microorganisms to be active. Nutrient release by microbial activity, in general, occurs over a fairly long time period. One potential drawback is that the organic fertilizer may not release enough of their principal nutrient when the plant needs it for growth.
Biosolids or dewatered sewer sludge is a recycled product of municipal sewage treatment plants. Two forms are commonly available: activated and composted. Activated sludge has higher concentrations of nutrients (approximately 5-3-0) than composted sludge. It is usually sold in a dry, granular form for use as a general purpose, long lasting, non-burning fertilizer. Composted sludge is used primarily as a soil amendment or horticulture material and has a lower nutrient content (approximately 1-2-0) because the microbial activity in the composting process has caused the loss of nutrients into the atmosphere.
Compared to synthetic fertilizer formulations, organic fertilizers contain relatively low concentrations of actual nutrients, but they perform important functions which the synthetic formulations do not. They increase the organic content and consequently the water-holding capacity of the soil. They improve the physical structure of the soil which allows more air to get to plant roots. Where organic sources are used for fertilizer, bacterial and fungal activity increases in the soil. Mycorrhizal fungi which make other nutrients more available to plants thrive in soil where the organic matter content is high. Organically derived plant nutrients are slow to leach from the soil making them less likely to contribute to water pollution than synthetic fertilizers.
There is concern with long term effects of using biosolids products in agriculture, particularly around edible crops, in the prior art. Possible negative effects varied with the origin of the biosolids and with the characteristics of the biosolids, for example, the level of disinfection that was applied to the biosolids prior to its usage and to the level of metals that were contained in the biosolids. Many commercial biosolids processing technologies produce what is classed by the United States Environmental Protection Agency as a Class B biosolids. This type of biosolids still has potential pathogens present because of the milder stringency permitted in the processing of these biosolids as compared to the high stringency Class A biosolids. The majority of biosolids processed in the United States in 2006 are still processed using Class B type protocols. A third concern regarding biosolids safety is their potential containment of personal pharmaceuticals or bio-active compounds such as antibiotics. Very few commercial biosolids processing methodologies have the mechanisms to eliminate these types of materials. Thus there is a need for safer organic fertilizers made from organic sludge.